In 1 Thess 3:6-10, Paul is encouraged in a time of distress. This refers to actual persecution Paul faced rather than the emotional distress he suffered as a result of being separated from the church. It is possible that Paul is continuing his metaphor, he was “orphaned” from his children and had no idea if they were safe, or if they were continuing to grow in their new faith.
Soon after Timothy and Silas join Paul in Corinth, Acts 18:6 indicates that Jews from the synagogue opposed Paul’s message. After Paul leaves the synagogue and forms a church (next door!), the Lord comforts him in a vision, telling him not to be afraid because no one will attack or harm him (Acts 18:9-11). The very next story is an attack by the Jews in which Paul is arrested and charged with worshiping God contrary to Roman Law (Acts 18:12-17). The proconsul Gallio throws the case out of court and Paul is not harmed in any way. In 1 Cor 2:3 Paul describes himself as coming to Corinth in “fear and much trembling.” In 2 Cor 6:3-10 and 11:16-29 he lists a number of times that he has suffered already. The letter to the Thessalonians was written in the midst of this suffering, just before Paul is given a vision comforting him (Acts 18:9-10).
But in the midst of this distress, Paul says that he “really lives” as a result of the news that the church is standing firm in the Lord. This is an odd expression, that “we really live knowing that you are standing firm.” The “we” would be Paul, Silas, and Timothy; the ministry team that founded he church.
What does he mean “live” (ζάω)? It is not that Paul would die if they had rejected the faith. What he probably means is that his life work is to plant churches and see them develop, it is what makes his life satisfying and gives him the encouragement to continue in the ministry. The image is that before the good news of Timothy’s report came, he felt dead, he was depressed about the situation he left in the church. But now that he has heard the good news of the report, he can live.
Paul was encouraged because the church was “standing firm in the Lord.” The syntax here is important: the KJV and the ESV translates the end of the verse as “if you stand” but the NIV (TNIV, NIV2011) has “since you stand.” The NIV attempts to reflect the grammar: the use of ἐάν with the present indicates that Paul understands the condition (standing firm) as a certainty. Grammatically it is a condition, but the first part of the sentence is so certain that it can be translated as “since.” (Use this as an example: “If it is Thanksgiving, we are going to eat pumpkin pie.” The condition is so certain, that we can say, “since it is Thanksgiving, we are going to eat pumpkin pie.”)
To “stand firm” (στήκω) means “to be firmly committed in conviction” (BDAG). The verb is formed from a perfect form of ἵστημι and is used by Paul standing in faith (1 Cor 16:13), in the Lord (Phil 4:1), or in the Holy Spirit (Phil 1:27). In Gal 5:1 and 2 Thess 2:15 is refers to holding on to the gospel as it was taught to the church by Paul in the past. There is a past event (their belief, their acceptance of the Gospel) which has some present effect (standing in their Lord).
Paul is therefore “revived” by the news that the church has not failed, in fact they have exceeded his expectations. The church is far from perfect, but they understand that they have not “arrived” and Paul praises them for wanting to grow even more.